Hybridoma antibodies that bind obligosaccharides are valuable reagents for analysis, localization, and purification of free oligosaccharides and glycoconjugates. We have developed immunization protocols and screening procedures, for producing hybridomas against oligosaccharides purified from human milk and urine. Many of these oligosaccharides are structurally identical with carbohydrate chains found in naturally-occurring glycolipids and glycoproteins. Hybridoma antibodies against a glucose-containing tetrasaccharide (G)4 with the structure GlcAlpha1-6GcAlpha1-4G1cAlpha1-4G1c have been used in a radioimmunoassay to study the metabolic origin of the ettrasaccharide. The same anti (G)4 hybridoma antibodies have been used for affinity purification of the free oligosaccharide. We also have prepared hybridomas against the milk oligosaccharide lacto-N-tetraose whose structure is identical to the Type I blood group precursor chain. Lacto-N-tetraosyl ceramide is a precursor to an "oncofetal" ganglioside. We are investigating the possibility that hybridomas against LNT may be useful for detecting products of gastrointestinal carcinoma cells which may be enriched in Type I precursor chains.